The overall goal is to provide a comprehensive description of the functional and structural development of neural inhibition in a central auditory nucleus of the gerbil (Meriones unguiculatus). The research plan can be divided into three specific areas: (1) Functional development. The developmental appearance of inhibitory and excitatory postsynaptic potentials will be quantified in lateral superior olivary (LSO) neurons, using the gerbil brain slice preparation. The latency, amplitude, and number of postsynaptic potential will be measured with standard intracellular techniques from animals of increasing postnatal age. (2) Anatomical development. The maturation of axonal arbors from a projection inhibitory nucleus, the medical nucleus of the trapezoid body (MNTB), to the LSO will be obtained by intracellular dye-filling of the processes. The absolute size, and the anatomical distribution of each arbor will be evaluated. Of particular interest in the two descriptive experiments, will be any indications of a lack of specificity during functional inhibitory contacts, exuberant axonal arbors). (3) Ontogenetic influence of neural inhibition. The developmental consequences of functionally eliminating the inhibitory projection to the LSO will be assessed in two ways. The effects of inhibitory activity on postsynaptic structure will be assayed by measuring LSO cell size. The effects on auditory function will be assayed by measuring the stimulus specificity of LSO neurons and the relative efficacy of the excitatory and inhibitory afferent pathways. These experiments will contribute to our understanding of the maturation of those auditory coding properties which rely on inhibition, and the degenerative changes in the central auditory system attendant to conductive and sensorineural hearing loss.